Expression of nitric-oxide synthase in rat Kupffer cells is regulated by cAMP.
Treatment of cultured rat Kupffer cells with lipopolysaccharide (LPS) resulted in a time-dependent increase in the expression of the inducible isoform of nitric-oxide synthase (iNOS). Agents that elevated intracellular cAMP levels (e.g. forskolin, dibutyryl cAMP, cholera toxin, and isoproterenol) markedly decreased nitrite production and iNOS protein formation by LPS-stimulated Kupffer cells. Furthermore, inhibition of LPS-induced nitrite formation and iNOS protein levels by these agents was enhanced in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. Forskolin, the most potent inhibitor of LPS-induced nitrite formation by Kupffer cells, decreased iNOS mRNA levels in a time-dependent manner. Time course studies indicated that forskolin was most effective at inhibiting LPS-induced nitrite formation and iNOS mRNA levels by Kupffer cells when added before LPS. Message stability studies established that forskolin did not enhance the rate of decay of LPS-induced iNOS mRNA. Nuclear run-on assays revealed that forskolin decreased LPS-induced transcription of the iNOS gene. Treatment of Kupffer cells with LPS induced the translocation of the p65 subunit of nuclear factor kappaB (NF-kappaB) into the nucleus, and this process was abolished by forskolin. In addition, the LPS-dependent degradation of IkappaBalpha was not observed in forskolin-treated cells; the levels of the p65 subunit of NF-kappaB were minimal in the nucleus at the same time. Also, we observed that forskolin induced transcription of the IkappaBalpha gene in a time-dependent manner and in addition up-regulated LPS-induced IkappaBalpha mRNA levels. Taken together, this study indicates that the attenuation of LPS-induced iNOS formation in Kupffer cells by elevated intracellular cAMP levels occurs by preventing the degradation of IkappaBalpha which suppresses the activation of NF-kappaB and inhibits the onset of transcription of the iNOS gene.
Mustafa
S B
SB
Department of Biochemistry, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284, USA.
Olson
M S
MS
D000818:Animals; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D020672:I-kappa B Proteins; D007728:Kupffer Cells / Q000166:cytology / Q000201:enzymology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000201:enzymology*; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000096:biosynthesis* / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D009573:Nitrites / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D012772:Shock, Septic; D014158:Transcription, Genetic / Q000187:drug effects
D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D008070:Lipopolysaccharides; D016328:NF-kappa B; C000606206:Nfkbia protein, rat; D009573:Nitrites; D012333:RNA, Messenger; D000072000:NF-KappaB Inhibitor alpha; D005576:Colforsin; D000242:Cyclic AMP; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat